Paging systems have been widely used for contacting paging users who are out of their office or otherwise not immediately accessible. Various message formats have been used in these systems to convey the messages from a caller to the paging user. Of these, voice paging has been widely used because a voice message provided the most complete information to the paging user, however, at the expense of a significant amount of air time. Tone only systems solved this air time problem by only alerting the paging user at the expense of providing only limited message information, such as "call your office" or "call home". More recently, numeric paging systems have provided increased information capability by transmitting a telephone number, such as "305-123-7787", which was displayed on the pager identifying the caller, while alphanumeric paging systems provided the capability of transmitting complete messages, such as "Call Joe at 305-123-7787" which was displayed on the receiver.
While prior paging systems have provided the paging user with the ability to select a message format suitable for his paging needs, the caller was not provided with a confirmation as to whether or not the page was received, especially when the paging user incurred considerable time to respond, as would often happen when the paging user was away from a telephone. One approach to solving the problem of confirming the paging user had received the message was to provide a real time voice talk back system. Such a system allowed the paging user to immediately respond with a voice message upon completion of receiving the message. The caller immediately knew the message was received, and if a response was not received, it was due either to the paging user being out of range, the pager being turned off, or the paging user being unable to immediately respond. In a system as described, once the paging user was able to talk back to the caller, the two were able to carry out a short two-way conversation. While both the paging user and the caller benefited from such real time talk back systems, it was generally at the expense of air time, the time to send the message, the time to deliver the response, and the time for any subsequent conversations. Since message throughput is a key factor in paging systems, such real time talk back systems were not widely promoted.
An alternative acknowledgment system, not requiring a voice response as in the talk back system, had been proposed which provided an acknowledge transmitter enabled by the paging user when a switch was actuated after receipt of the message. The transmitted acknowledge signal, when received at the paging terminal, initiated a canned voice response from the terminal to the caller indicating the message was received and understood. An immediate response to the message was necessary by the paging user if system throughput was to be maintained and only a limited number of canned responses were provided within the terminal.
Neither system described took into account the problems presented by dynamically varying system loading, and as a consequence, throughput was sacrificed for the capability to provide acknowledgment.